Power supply

ABSTRACT

A pulsed power supply for providing power to a piezoelectric crystal. The power supply provides power to the piezoelectric crystal causing contraction of the crystal. Upon reaching a predetermined degree of contraction, the electrical voltage form the power supply is removed from the piezoelectric crystal by creating a short-circuit between the power supply and the crystal. Removal of electrical voltage from the crystal causes the immediate expansion of the crystal and a resulting energy wave.

BACKGROUND OF THE PRESENT INVENTION

1. Field of Invention

The invention relates to an improved apparatus for the contact freedisintegration of a calculus located in the body of a human being. Inparticular, the invention provides improved localization of the calculusand enhances the ability to direct a focussed sonic wave to a targetregion in the body.

2. Prior Art

Extracorporeal shock-wave lithotripsy in a medical procedure thatdisintegrates renal (kidney) stones. The term, lithotripsy is derivedfrom the Greek and literally means "stone crushing." This medical "stonecrushing" technique has been demonstrated to be effective on renal(kidney), upper ureteral and biliary stones (gallstones) in humanpatients. The technique is noninvasive and eliminates the need for themore conventional stone removal procedures, such as open surgery.

Stone crushing is achieved by the geometric focussing of energy, suchthat the area of focus coincides with the stone that is to be shattered.The focussing of energy is a principle that is frequently used to obtaina strong effect within a confined area. The application of focussedenergy is effective on the stone, since it is relatively brittle. Theapplication of stress leads to the rapid information of cracks andeventually to the disintegration of the stone.

Although a single intense pulse will generally shatter the stone, apulse train of lower intensity and short duration pulses will generallyproduce smaller and more uniform particles. One drawback to a series ofpulses is that during treatment the small particles produced during thefragmentation shock waves may obscure the larger remaining fragments.This may result in the shielding of the larger, remaining fragment fromthe shock wave, which results in an increase of treatment duration.

On the other hand, the accumulated small particles may lead the careprovider into prematurely terminating treatment before completion, dueto the inability to accurately view the remaining larger fragments.

Another problem associated with the production of small particles, isthat gravitational forces may cause the small particles of settle intothe lower calyces, thereafter requiring an excessive amount of time toeffectuate clearing these lower calyces.

Despite the problems associated with the smaller particles, for thekidney stone patient, there are number of direct benefits from thelithotripsy technique that outweigh these minor disadvantages. Thetechnique is capable of reducing the length of hospital stay from 7 to14 days for conventional stone removal surgery to 4 days or fewer. Italso eliminates the 4 to 6 weeks post-hospitalization convalescencecommonly required after major surgery. Typically, the kidney stonepatient will naturally and spontaneously pass the stones in the urine,much as if the stones were naturally grain-sized. However, afterfragmentation, there will be many more grain-sized stones than occurnaturally.

There are several other techniques presently used to treat kidneystones, as an alternative to major surgery. For example, if the stoneremains grain-sized, it usually passes spontaneously in the urine andthe patient can be treated with drugs to reduce the pain and to preventfuture stone occurrence. However, this technique is usually onlyeffective for very small stones.

Depending on the size and the location of the stone, several otherclinical and surgical methods are available. If the stone has formed orlodged itself in the lower urinary tract and bladder, a standardcystoscope combined with a stone basket or a special stone removalforceps may be used to extract the stone. During the procedure, a localanesthetic must be administered to minimize the pain. Additionaldrawbacks are the possibilities that the ureter will be damaged and theformation of additional stones that would prohibit the repetition of theprocedure.

Ultimately, if the stone cannot be removed by any of the conventionalmethods, the patient must resort to open surgery. The traditionalsurgical procedure is a major operation that requires an incision intothe kidney or ureter to remove the stone. In addition to the normalmorbidity and risks associated with major surgery, another stone couldform, necessitating further surgery. Furthermore, there is a chance thatthe patient will finally lose the kidney altogether.

As an alternative to open surgery, lithotripsy was explored. However,early lithotriptic treatment employs invasive ultrasonic lithotripsy.The lithotriptic means employed involved an insertion of an ultrasonicprobe into a small incision in the patient's side. While this requiredless recovery time than traditional surgery, it was still surgery,however small the incision and furthermore carried all the inherentrisks associated with surgery.

Noninvasive extra corporeal shockwave lithotripsy was developed andovercame the negative risks of surgery. A shock wave is generated andultimately focussed at the stone. The focussed wave strikes the stone,it disintegrates the stone and the stone fragments are ultimately passedthrough the ureter.

Early versions of extra corporeal (EC) shock wave lithotripsy requiredthe patient to be immersed in a large tank of water. Originally, a sparkgap electrode was fixed at one end of a large stainless steel tub andgenerated a shock wave as the electrode was discharged underwater. Sincethe impedance properties of water and soft tissue are similar, theshockwave entered the body without damaging the soft tissue. If care istaken to direct the shockwaves at the calculi, other parts of the bodyare generally not affected. Typically, bones are not affected by thisprocedure due to their high tensile strength and the brevity of thepulses. However, the large difference in acoustical impedance betweenthe water and the stone results in enough pressure to shatter the stone.The process was painful and the patient generally required an epiduralor general anesthesia.

Before treatment could commence, it was necessary to locate and identifythe stone. Prior to immersing the patient into the large stainless steeltank of water, the patient was x-rayed thus prelocalizing the stone.After every 100 pulses or so, the patient was lifted out of the tank andx-rayed again. This was to ascertain the status of the stone and toverify the effectiveness of the treatment. With an average of 1600pulses, the patient could be x-rayed as many as 17 times to verify thatthe stone was fragmented and to confirm the completeness of thetreatment. Although an x-ray produces a sharper and clearer progessreport, the patient was required to undergo a number of detrimentalradiation exposures.

Another problem associated with immersing the patient is the inabilityto accurately reposition the patient once the patient had been moved.Since the electrode is fixed, the patient must be positioned andrepositioned. This led to inaccuracies and sometimes painful results.

An alternative localization technique requires the use of two x-rayimages, with the focal point at the central point of the two screens.Typically, the two x-ray devices for locating the stone are disposednext to the shockwave generator and reflector and are on an oppositeside or axis of the generator. The two central beams of the two x-rayheads intersect the axis of the reflector running through the two focalpoints. The intersection should be near or at the location of the stone.Establishment of a relationship between a spatially fixed mark and thepatient is required. The equipment generally is repositioned vis-a-visthe patient.

From a point of view of expense, the utilization of two x-ray head anddevices is relatively expensive to operate and to maintain. There isalso the question of the radiation dosage that the patient receives.

When using an x-ray procedure, the patient must be positioned orrepositioned such that the stone is located at the focal point of theshock wave. For example, when using a stainless steel water tank, thepatient is then positioned with a hydraulic system so that the calculusis at a predetermined focal point. While this allows access to a moreaccurate target region, it is necessary to physically reposition thepatient for each image. Disadvantageously, the patient is required toremain immobilized during the location procedure.

Ultrasound imaging is another suggested alternative means of locatingand monitoring the stone. Generally for well-defined stones, ultrasoundis sufficient to monitor the progress of treatment. Furthermore, the useof ultrasound eliminates the problems of radiation dosage that arisewith the use of x-ray localization techniques.

Another advantage of ultrasound imaging is the ability to monitor realtime progression of the treatment. Additional ultrasound monitors can bepositioned within the treatment system in such a way as to virtuallyeliminate repositioning of the patient.

However, ultrasound imaging does not provide the same same high contrastresults or "pictures" that an x-ray unit can provide. Since theresulting images are not as sharp and have as high a contrast, which canbe due to the limitations to the technique itself, the size and quantityof the stones, or the size of the patient, can make progressivemonitoring of patient and the subsequent treatment somewhat risky andhaphazardous.

Furthermore, prior to the elimination to the large steel water tank, theuse of ultrasonic monitoring equipment was severely limited, as theequipment had to be located within the vicinity of the patient itself.

A combination of the two monitoring techniques, that is x-ray andultrasound, would be suited except for the problem of patientrepositioning. Immobility of the patient is essential and are identicalto the problems discussed previously in connection with the x-raytechniques.

The eventual elimination of the large stainless steel water tankresulted in a more compact and effective system. Furthermore,elimination of the water tank also gave rise to the possibility of usingultrasound imaging. Patient immersion became unnecessary as the acousticwaves were still propagated through a water containment bag rather thanthrough an open body of water. The patient is positioned over a cushionor a bag filled with water. The cushion is coupled to a stretcher and tothe patient by a layer of ultrasound gel.

Once the patient positioning had been improved, the means for producingthe shock wave needed to be improved. For example, the prior method ofproducing focussed acoustic waves required an electric dischargegenerated across an underwater spark gap, positioned in the focus lineof an elliptical reflector. The early spark gap systems generated ashockwave in a large tank of water, in which the patient had previouslybeen positioned. The process shattered renal stones by a brute forcemethod. The treatment required the patient to have an epidural, spinalor general anesthesia in order "to keep the patient under control, toavoid hurting the patient and to aim better at the stone."

Improvements made it possible to remove the patient from the water tankand to virtually eliminate the need for an epidural or generalanesthesia. Generally, a larger ellipsoid for focal precision and adecrease in the power output are credited for the improvements. Accuracyimproved as the focussing process was computer controlled, rather thanvisual sighting by the operator. The computer automatically positionsthe patient in the shockwave focus by controlling the patient's table.

The spark gap systems create a diverging pulse or explosion. The energyproduced is distributed over a relatively large area, for example 15-20mm square and requires that the energy be focussed within a parabolicreflector. This diverging pulse induces arhythmia, pulverizes tissue andcauses bruising. To avoid the inducement of extrasystoles, the shockwavemust be released as a function of ECG or respiratory triggering.Furthermore, the spark gap electrodes tend to be somewhat costly.

On the other hand, an alternative means using a piezoelectric transducergenerates a converging pulse and eliminates the need for cardiac orrespiratory triggering. With a converging pulse system, an area ofimpact of approximately 2-3 mm square is observed. This results in lesstissue damage with approximately the same amount of pressure. Generally,the patient only requires a local or a topical anaesthetic, if any atall.

The piezoelectric crystal is the basis for the piezoelectric transducer.A piezoelectric crystal is a piece of natural quartz or other asymmetriccrystalline material capable of demonstrating the piezoelectric effect.Piezoelectricity is a phenomenon first noticed in 1880 whereby certaincrystalline substances generate electrical charges when subjected tomechanical deformation. The reverse effect also occurs, that is, avoltage applied across the crystal causes mechanical deformation orflexing.

To produce the shock wave, a piezoelectric crystal is deformed byapplying a high frequency, high voltage pulse of the proper polarity,thus causing the crystal to compress. The voltage is then withdrawn fromthe crystal, such as shorting the crystal to ground and the crystalexpands to it's "normal" state. This results in a pressure wave frontthat propagates through a medium such as water.

Typically, the shock wave is focussed by arranging piezoelectric crystalelements in a mosaic pattern on the surface of a dish generally shapedas a concave lens. The pattern and lens may be designed such that eachindividual element is excited by a pulse generator simultaneously. Thus,the waves produced by the crystals arrive at the target area focussedand in phase, with a very narrow near ideal shape and with high energyat the focal point. Advantageously, the dish is shaped to produce verysmall focal areas in which the energy is sufficient to destroy the storebut virtually painless.

A major disadvantage of the multi-element piezoelectric system is thenecessity of simultaneously triggering 300 to 3000 elements on theconcave surface of the focussing lens. Disadvantagely, it is necessaryto connect all the piezoelectric crystals to act as one to work inconjunction with a single power supply. An alternative method is toconnect each individual element to individual power supplies, forexample, having 300 elements and therefore 300 very small, individualpower supplies triggering simultaneously. In addition to the problemsarising from coordinating all the elements, there is the problem of costeffectiveness.

Another costly disadvantage is the requirement that the numerouselements be specially made. The individual elements must be contoured tofit within the concave configuration of the focussing lens. Thisdecreases the cost effectiveness of the piezoelectric system.

With the use of a piezoelectric transducer, it is necessary to generatea sufficiently high voltage to deform the piezoelectric crystal.Typically, a high voltage generator is required.

In order to ensure that the shockwave generated from the piezoelectriccrystal deformation is sufficient to crush the kidney stone, the wavemust be focussed. One alternative means of focussing the wave is tocreate a semi-circular dish wherein the piezoelectric crystals arearranged on the upper surface of the dish in a spherical mosaic-likearrangement.

Generally this type of arrangement requires careful manufacturing of thecrystals such that the bottom is rounded as well as the top to maintaina semi-spherical or semi-ellipsoid surface area. Either the crystals canbe manufactured so that they fit like a mosaic within the face of thelens or dish or they may be sufficiently small pieces that, because oftheir size, they merely fit within the shape of the dish itself.

A focussing lens with the crystals configured within the concave surfaceof the lens produces a very narrow, more ideal shape with a high energywave at the focal point. This narrowed focussed shockwave requires ashorter duration for the shattering pulse.

The use of a focussing lens with the piezoelectric crystals has severalother advantages over that of the spark gap technology. Since the lenscreates a converging focussed pulse, the problem of cardiac gating orarhythmia may be eliminated. In contrast, the spark gap generatorscreate a diverging pulse and induce arhythmia. Additionally, there canbe much more damage to surrounding tissue as well as substantialbruising and the possibility of passing of blood through urine whenusing ellipsoid reflectors.

Thus, what is needed is a lithotripsy system for production of afocussed energy wave including a improved power supply for providingvoltage to piezoelectric crystals.

SUMMARY OF THE INVENTION

The present invention discloses an lithotripsy system having an improvedpower supply for supplying pulsed power to a piezoelectric crystal. Thecrystal responds to application of voltage from the voltage source bycontracting. Upon removal of the voltage from the voltage supply, thecrystal expands creating a energy wave in front of the crystal. In thepreferred embodiment, the energy wave is focussed with a focussing dishand directed for application to a calculus in a living body. Thisresults in the destruction of the calculus.

The power supply apparatus of the present invention comprises a triggerpulse generation for generating trigger pulses. Generation of eachtrigger pulse results in the eventual production of a focussed energywave.

The trigger pulse generator is coupled with a voltage supply forsupplying voltage to the piezoelectrical crystal. Responsive to eachtrigger pulse, the voltage supply produces a ramped voltage which isapplied to the crystal.

In addition, the ramped voltage is applied to a spark gap tube which,upon application of a predetermined voltage level, causes the voltagesupply to short-circuit removing power from the crystal; this removal ofpower results in the immediate expansion of the crystal and subsequentproduction of an energy wave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a lithotripsy system of the preferredembodiment of the present invention.

FIGS. 2(a)-(c) are schematic representations of the relationship betweenseveral components of the lithotripsy system and:

(a) a representation of a body of a patient to an x-ray component of thelithotripsy system; and

(b) a representation of the body of the patient to an ultrasonic-realtime scan component of the lithotripsy system; and

(c) a representation of the body of the patient to a ultrasonicshockwave generation component of the lithotripsy system.

FIG. 3 is a perspective view of a patient table and dual tomo-heads ofthe x-ray component of the lithotripsy system of the preferredembodiment.

FIG. 4 is a cross-sectional representation of a control unit and a stonebreaking unit of the lithotripsy system of the preferred embodiment.

FIG. 5 is a detailed top plan perspective view of an acoustical lensassembly of the lithotripsy system of the preferred embodiment.

FIG. 6 is a cross-sectional view of the acoustical lens assembly takenas section A--A of FIG. 5.

FIG. 7 is a bottom plan, exploded, perspective view of piezoelectricalcrystals bonded to the acoustical lens and of coupling copper mesh.

FIG. 8 is a circuit diagram of a piezoelectric crystal triggeringcircuit as may be utilized by the lithotripsy system of the preferredembodiment.

FIG. 9 is a graphic representation of the timing sequence of thetriggering circuit of FIG. 8.

FIG. 10 is a graphic representation of the voltage profile from acrystal of FIG. 8.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

An invention is described that provides a means for locating,positioning and for breaking up, without contact, calculi present in thebody of a human being. As a result of the capabilities of the presentinvention, the accuracy and completeness of lithotriptic treatment areeffectively enhanced. In the following description, numerous specificdetails are set forth such as specific dimensions, materials, etc., inorder to provide a thorough understanding of the present invention. Itwill be obvious, however, to one skilled in the art that the presentinvention may be practiced without these specific details. In otherinstances, well-known procedures and materials have not been describedin detail in order not to unnecessarily obscure the present invention.

Proceeding now to the detailed description of the drawings, FIG. 1illustrates a perspective overview of the lithotripsy system 100 of thepresent invention. The lithotripsy system 100 is comprised of anultrasound imaging unit 125, a mobile x-ray unit 126 and a lithotripterunit 127.

The ultrasound imaging unit 125 is a self-contained system that can beutilized as a stand alone ultrasound unit, in addition to functioning asa real-time ultrasonic imaging system for the lithotripter 100. Theultrasound imaging unit 125 is comprised of a control panel 600, ahand-held imaging probe 110, and a monitoring unit 109.

The x-ray unit 126 provides for fluoroscopic image processing and spotfilm capabilities. A urological table 113a is docked to a lithotriptertable 113b and locked into place by the docking latch 112. Although thepreferred embodiment illustrates the use of docking latch 112, any meansof stably connecting the two tables together is within the spirit andscope of the present invention. Alternatively, the use of only a singletable is also within the scope of the present invention. The urologicaltable 113a can be used as a stand alone examination table for routineurological procedures with or without the use of the x-ray unit 126.

The x-ray unit 126 is comprised of mobile C-arm 111, a pair of fluoroexposure monitors 106, a control unit 105, and a monitor cart 104.Although FIG. 1 preferably illustrates a mobile C-arm 111 as a means forproviding fluoroscopic images, a standard x-ray unit is also anacceptable means of providing the necessary fluoroscopic images. Themobile C-arm 111, as well as a standard x-ray unit is typicallycomprised of a tomo head 101 and a means for receiving fluoroscopicimages 102.

Referring to FIGS. 2(a)-(c), the treatment procedure of the lithotriptersystem 100 of FIG. 1 is schematically shown. FIG. 2a describes thepatient P in relationship to the tomo head 101 and means for receivingflouroscopic images 102. The patient P is positioned on a planarsurface, with the upper portion of the body inclined upward on aheadrest 201. The lower portion of the body is immobilized by placingthe patient's knees over a leg rest 202. A dual fluoroscopic image isthen obtained by acquiring two oblique images. The oblique images areobtained by moving the tomo-head 101 off axis by +9 degrees and -9degrees.

FIG. 2(b) describes the patient P in relationship to an acoustical lens205 of the lithotripter unit 127. (The acoustical lens 205 will bedescribed in more detail with reference to FIGS. 5-7.) The patient P,still positioned on the planar surface and the headrest 201 and leg rest202 are moved from one end of a treatment table to the other end of thetable. An ultrasound probe 206 is positioned centrally within the lens205. A focussed shockwave 207 is directed at the kidney stone previouslylocated by the dual fluoroscopic images as described in FIG. 2(a). FIG.8 describes the pre-location procedure in more detail.

FIG. 2(c) describes the patient P in relationship to an ultrasoundimaging probe 206 of the lithotripter unit 127. The imaging probe 206is, preferably, centrally located in the acoustical lens 205, allowingfor ultrasound localization and real-time monitoring. The centrallocation of the imaging probe 206 provides a multi-zone focussing array208 allowing for an extended field-of-view.

Referring to FIGS. 1 and 3, the lithotripsy table 113b docked to theurological treatment table 113a and the x-ray unit is illustrated. Thetwo tables 113a and 113b are docked and then latched together forstability providing a platform for a moveable planar surface or a "sled"107. The docking latch 112 is dropped into place once the tables aredocked together. Although the preferred embodiment describes the use ofa docking latch 112, any functionally equivalent latching means may beused so long as the latching means provides stability for the tables andallows the use of the sled 107.

To initially locate the kidney stone X, the patient P is placed on thesled 107. The sled 107 is located at position 1, which is at theurological table 113a. During the localization procedure, the patient Pmust remain essentially immobile. Immobility is achieved by locking thesled 107 into position and by the careful placement of the patient P.The upper portion of the patient's body is positioned against a headrest201, while the patient's legs are placed over the leg rest 202. Thisallows the patient's back to rest directly and comfortably on the uppersurface of the sled 107. In addition to the relative comfort, thepatient is made immobile.

Once the patient P is placed such that the kidney stone X is generallycentrally located over the fluoroscope 102, a fluoroscopic exposure istaken of the stone X. The precise position of the stone X is achieved bytaking two x-ray views with the tomo head 101 at a +9 degee obliquesetting 101a and a -9 degree oblique setting 101b. After the two obliqueviews are acquired, the processing unit of the x-ray control unit 105,shown in FIG. 1, calculates the coordinates of the stone X within thebody.

Initially, the stone X is marked on the dual monitors 106 with a markingsymbol, such as a cross-hair marker. The coordinates are then calculatedwith reference to radiopaque markers embedded in the surface of table113a. After the coordinates have been calculated, the patient P is movedinto position 2, via the sled 107, onto the lithotripter housing 103.The sled 107 is then locked into position. The stone coordinatesobtained from the x-ray prelocalization are sent to the lithotripterunit 127 for positioning the stonebreaker focal point.

FIG. 4 illustrates the positioning of the acoustical lens 205 andstone-breaking assembly 301 within the lithotripter control housing 103.

In the preferred embodiment, the housing 103 is provided with wheels310, thus increasing the mobility of the lithotripter system 100.However, the wheels 310 are not essential to the practice of the presentinvention.

A portion of the housing 103 is utilized by the several electroniccontrol units. A system controller 307, a pulse modulator 306, a servoamplifier 308 and the servo control unit 309 are located within thehousing 103. All of the units are typically constructed from well-knownprior art circuitry and sequences.

The servo control unit 309 drives the servo amplifier 308, which in turncontrols a positioning system 303. The control unit 309 employsalgorithms consisting of prior art sequences typically used to controlrobotic mechanisms. The positioning system 303 controls the positioningof the stone-breaking assembly 301 in manner similar to the computercontrol of a robotic arm. The use of robotic algorithms with thepositioning system 303 virtually eliminates patient handling, since a5-axis positioning of the acoustical lens 205 is now available. Theability to rotate or otherwise position the focussed shock waveadditionally aids in the minimization of pain and the shortening oftreatment duration. Thus, for example, if a kidney stone is found to liein close proximity to a rib, the positioning system 303 is able tocompensate and rotate to an alternative position, thereby avoiding therib.

Additionally, the housing 103 also functions as a base for thelithotripter table 113b. An area located directly over a flexible watercontainment enclosure (waterbag) 302 is open, providing for directpatient contact with the water bag 302. The patient's back is positionedover the water bag 302, allowing the weight of the patient to force thebag 302 downward causing the waterbag 302 to conform to the shape of thepatient's back. This provides necessary coupling between the water bag302 and the patient so that the shockwaves propagated through the waterbag 302 will travel uninhibited to and through the patient's body,ultimately shattering the kidney stone.

Referring to FIG. 5, the stone breaking apparatus 301 is illustrated.The assembly 301 is comprised of the acoustical lens 205, apiezoelectrical crystal array 405, a coupling means 407, a mechanicalstandoff 403 and a supporting back plate 404.

The acoustical lens 205 is fabricated in the shape of an ellipsoid. Inthe preferred embodiment, the lens 205 is shaped from a singular pieceof aluminum alloy. However, other materials could be used that havecharacteristics that allow the propagation and focussing of energy frompiezoelectric crystals and still be within the scope and spirit of thepresent invention.

The shape of the lens 205 is generally ellipsoid, such that the concaveinside surface 408 is defined by the following equation:

    y=13.525-(182.931-1.060 x.sup.2).sup.1/2

The lens 205 of the preferred embodiment measures approximately 18.75inches from flange to flange with a depth of approximately 3.95 inchesfrom top to bottom. A center opening 401, allows for placement of anultrasonic probe approximately 3.31 inches in diameter. The stonebreaking apparatus 301 is provided with an upper flange 402, whichallows the lens 205 to be positioned within the apparatus 301 itself.The assembly 301 is held together with a supporting back plate 404.

Referring to FIG. 6, section A--A of FIG. 5 is illustrated. The waterbag 302 is illustrated to show its relationship to the acoustical lens205. The acoustical lens 205 is positioned such that the water bag 302positioned directly on the concave upper surface 408 of the lens 205.The back support plate 404 holds the stone breaking apparatus 301together.

In the preferred embodiment, the water bag 302 is comprised of twoindependent bags. There is an inner bag 1 that is attached by beingpinched between the top lens flange 402 and a ring, which is thensecured to the lens 205 with screws. The outer bag 2 is secured to theoutside diameter of lens 205 with a hose clamp-line strap. This outerbag 2 serves as a back up seal in case the inner bag 1 should rupture.

Positioned on the bottom surface of the acoustic lens 205 are thepiezoelectric crystals 405. In the preferred embodiment, thepiezoelectric crystals 405 are circularly arranged in an array ofapproximately 720 square pillars or elements. The preferred embodimentpresently uses a C5800 ceramic for the crystals 405. However, anyceramics demonstrating the same or functionally equivalentcharacteristics may be used and still be within the spirit and scope ofthe present invention.

After piezoelectric crystals 405 have been bonded to the bottom surfaceof the lens 205, the crystals 405 are encapsulated. This provideselectrical insulation and seals the crystals 405. Typically, a genericmaterial such as an RTV silicon elastomer is used to encapsulate thecrystals 405.

An acoustical matching layer 410 may be placed on the concave surface408 of the lens 205. The matching layer 410 may comprise a generic typeof epoxy or plastic used to provide a better acoustic impedance matchbetween the lens material and the water. Of necessity, this material isdependent on the lens material. Although the acoustic matching layer 410is illustrated in the preferred embodiment of the present invention, isit not essential to the practice of this invention. However, the epoxyor plastic when used, needs to have similar matching characteristics tothe material selected for the lens 205. Advantageously, this layerreduces the sharp transition zone at the water/lens interface.

Referring now to FIG. 7, a perspective view of the piezoelectriccrystals 405 mounted on the bottom surface of the acoustical lens 205 isdescribed. After the lens 205 has been fashioned, the piezoelectriccrystals 405 are positioned. In the preferred embodiment, the crystals405 are positioned in a circular array similar to a mosaic, ofapproximately 720 square pillars. Each pillar occupies an area of 0.09square inches. The volume is approximately 0.045 cubic inches.Alternatively, a single large crystal may be shaped to cover the buttonsurface of the lens 205. As a third alternative, several larger piecesmay be utilized. However, the preferred embodiment provides 720 pillarsto allow for easier replacement of blocked pillars. The arrangement ispreferred since a broken pillar is much easier to replace. The mosaic ofcrystal pillars decreases the lateral stress and if any one of thepillars should crack, the crack will not propagate through the entirepiezoelectric crystal 405 array. In the preferred embodiment, thecrystals 405 are bonded to the bottom surface of the lens 405 using anadhesive available under the trade name of Emerson Cummings 1264 Epoxy.

Once the crystals 405 are positioned, all the pillars are wired inparallel providing for parallel exitation from a single power supply.The parallel wiring is accomplished by placing a voltage coupling meanson the bottom of the crystals 405. In the preferred embodiment, a coppermesh 409 is bonded to the top of the crystals 405 using a silver epoxy.However, any voltage coupling means accomplishing the same objective maybe used and still be within the scope of the present invention.

To produce a shockwave sufficient to shatter a kidney stone, thepiezoelectric crystals 405 must be exited. FIGS. 8-10 illustrate thecrystal triggering circuit, the resultant wave form and the timingsequence for the triggering pulse.

Referring to FIGS. 8 and 10, a voltage supply 501 is used to excite thepiezoelectric crystal 508. The voltage supply 501 of the preferredembodiment is a Phazon model PM3020A. The voltage supply 501 is coupledto a hydrogen spark gap tube 503, the inductor 504 and the piezoelectriccrystal 508. The pulse generating circuit for the spark gap tube 503 isdescribed in FIG. 9. Although a Phazon model PM3020A is used in thepreferred embodiment, and voltage supply or ramp source having similarcharacteristics would be acceptable for use with the present invention.The voltage supply 501 provides a constant current source manuallyadjustable from 1 to approximately 60 milliamps. Furthermore, thevoltage supply provides an output voltage range of to 160 VDC inapproximately 128 equal steps with a tolerance of a +/-3% of setting.The output current is adjustable within the range of 0-25 milliamps. Thecurrent must and is stable within a +/-3% of the set current. Transientresponse is less than 2 milliseconds. The voltage supply provides for aninput line frequency of 47-67 hertz. Furthermore, the supply 501comprises an under voltage protection.

The initial trigger pulse comes from the controller panel 600 of thelithotripter system 100. The trigger pulse controls the ramp output ofthe voltage supply 501. When the voltage supply 501 receives the triggerpulse, the voltage supply turns on and ramps up to a predeterminedvoltage. As the voltage supply ramps, the voltage across the capacitiveload, which in this case is the crystal 508, follows a similar rampprofile. Additionally, the spark gap tube 503 encounters a similar rampvoltage. Once the voltage across the spark gap tube 503 has reached itscharacteristic ionization voltage, the spark gap tube 503 triggers,creating a short circuit between the spark gap tube 503, an inductor 504and the crystal 508. When the spark gap tube 503 triggers, a delayedreset pulse is sent to terminal 502. This allows the spark gap tube 503to be reopened following the discharge of the stored current into thecrystal 508. This permits a second pulse or any additional pulses withminimal time delay.

FIG. 9 illustrates a timing diagram of the pulse sequences used fortriggering the spark gap tube 503 and the piezoelectric crystal 508.Pulse sequence A illustrates the initial triggering pulse from thecontroller 600. Sequence B illustrates the ramp up of the voltage supply501. Sequence C illustrates the corresponding ramp up of the spark gaptube 503. Sequence D shows the generation of the time delay initiated bythe firing of the spark gap tube 503. Following this time delay, a resetpulse is sent to the spark gap tube 503 via terminal 502.

FIG. 10 illustrates corresponding voltage ramp across the crystal 503 asthe voltage supply ramps. A crystal absorbs the voltage, flexingcontinuously until the spark gap tube 503 triggers. Once the tube 502 istriggered, the output voltage across the capacitive load of the crystal508 is rapidly discharged through inductor 504. The reduction of thevoltage on the crystal 508 from its peak 510 to its relaxed state 511should be essentially instantaneous.

This is because the crystal 508 will instantaneously return to itsnormal relaxed state when the voltage is removed from across the crystal508.

An advantage of the pulsing circuit of FIG. 8 is that due to therelative slow ramp time of the voltage supply and the crystal 508 thereis minimal stress applied to the crystal 508 until just prior totriggering.

The slow, continuous ramp provides for a continuous rate of"deformation" of the crystal 508. This is opposed to a rapid deformationof the crystal 508 which could result in premature triggering.Furthermore, when the voltage across the crystal 508 is removed, thetheoretical circuitry should affect an instantaneous return to thenormal relaxed state of the crystal. To effect a rapid discharge of thecrystal voltage, inductor 504 is chosen to produce a critically dampcircuit, with the resistance of such a circuit being the intrinsicresistance of the crystal 508. In the preferred embodiment, the inductor504 is approximately one microhenry. Once the voltage is removed fromthe crystal 508, this instantaneous return to the normal state producesa disruptive or sonic wave front. This wave front is propogated throughthe acoustical lens 205 focussing to a narrow focal point coincidentwith the kidney stone, thus providing the necessary energy to shatterthe kidney stone.

Thus what is described is a lithotripsy system having an improved powersupply for energizing piezoelectric crystals.

We claim:
 1. In a lithotripsy system having a piezoelectric means forgenerating an energy beam upon expansion and a focussing means forfocussing said energy beam on a calculus in a patient, said focussingmeans attached to said piezoelectric means, the improvement comprising ameans for supplying power to said piezoelectric means, said power supplymeans comprising:a trigger pulse generating means for generating atrigger pulse; voltage supply means, coupled to said trigger pulsegenerating means, for generating a ramped output voltage upon receivingsaid trigger pulse; said piezoelectric means coupled in parallel withsaid voltage supply means and contracting as said ramped output voltageis received; and a spark gap tube means, coupled in parallel with saidvoltage supply means, for creating a short circuit when said rampedoutput voltage reaches a predetermined level thereby rapidly decreasingthe voltage across said piezoelectric means causing said piezoelectricmeans to expand thereby generating said energy beam.